А) 2cos13*cos43-cos56/2sin58cos13-sin7 1 б) 2cos10*cos70-cos80/2sin40cos10-sin5 0

1)2cos13cos43-cos(13+43)=2cos13cos43-cos13cos43+sin13sin43= =cos13cos43+sin13sin43=cos(43-13)=cos30=√3/2 2sin58cos13-sin(58+13)=2sin58cos13-sin58cos13-cos13sin58= =sin58cos13-cos13sin58=sin(58-13)=sin45=√2/2 (2cos13*cos43-cos56)/(2sin58cos13-sin71)=√3/2: √2/2=√3/2*2/√2=√3/√2=√6/2 2)2cos10cos70-cos(10+70)=2cos10cos70-cos10cos70+sin10sin70= =cos10cos70+sin10sin70=cos(70-10)=cos60=1/2 2sin40cos10-sin(40+10)=2sin40cos10-sin40cos10-cos40sin10= =sin40cos10-cos10sin40=sin(40-10)=sin30=1/2 (2cos10*cos70-cos80)/(2sin40cos10-sin50)=1/2: 1/2=1

система:   1) 2x+3y=-4     2)x-y=-7

 

1)2(-7+y)+3y=-4

2)x=-7+y

 

1)-14+2y+3y=-4

2)x=-7+y

 

точка пересечения прямых :   (-5; 2)